The present invention relates to a magnetic storage device, and in particular to a digital information storage device used in a digital recording apparatus such as a magnetic disc device and a magnetic tape device.
In a device of the prior art, information is read from/written into a vertical recording medium through a ring-type head as described in IEEE Transactions on Magnetics, Vol. MAG-21, No. 5, pp. 1365-1367 September 1985. In general, the medium is not provided with a high permeability film on several occasions.
In this case, a change in the magnetic flux passing through the magnetic core of the head is detected by a coil wound around a magnetic core. The leakage flux generated from magnetization transition recorded on the medium passes through the core along a window for winding. This unadvantageously results in an elongated magnetic circuit of the leakage flux and in increased magnetoresistance, the reproduction efficiency being lowered.
In a device of the prior art described in JP-A-59-40315, information is read from/written onto a vertical recording medium having double layers through a single sided single pole type head.
In this case, the main pole of the head is thin in thickness, resulting in low efficiency. Further, the nonuniformity in the height of the main pole directly exerts this advantageous influence upon the efficiency.
Further, such a known example of the prior art has drawbacks described below in addition to the above described lowering of the reproduction effciency caused by the long magnetic circuit of the leakage flux.
As shown in FIG. 3, magnetic characteristics (B-H characteristics) 29 of a vertical recording medium measured in a direction perpendicular to the medium surface are excellent in squareness. The magnitude of magnetization in the vicinity of the recorded transition which has important relation to the magnetic recording characteristics assumes a value 34 less than Br because of a demagnetization field 31 is generated from magnetization at the recording medium surface. In case of the double layered medium described in the aforementioned known example as well, the magnetization is decreased lower than Br by a demagnetization field 31 which is weakened by a high permeability layer. In case of a single layered medium, a demagnetization field 30 which is approximately twice in magnitude that of the double layered medium is generated since high permeability layer is not present. Thus the residual magnetization also assumes a smaller value 33. A smaller value of residual magnetization results in a smaller reproduced output. Therefore, the decrease in residual magnetization due to the demagnetization field poses a problem.